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dissolved lighter alkanes from the water column, as opposed to the heavier fraction
found in the surfaced oil, emphasizing the importance of examining the specific
composition of petroleum components to understand oil transport (Boehm and
Fiest 1979).
However, not all spills from offshore platforms involve subsea releases. The
Montara H1 well in the Timor Sea off the northwest coast of Australia blew out in
2009, releasing approximately 4,000 tonnes of oil over 74 days (Spies et al. 2017)
and producing a surface slick that was reported to travel approximately 35 km from
the location of the release (Burns and Jones 2016). However, unlike the previously
discussed deepwater releases, the release of this oil was from the platform above the
surface of the water, and hot oil and associated gas were exposed to the air before
reaching the water surface. Despite the released oil being classified as a light crude
(API gravity 34.6), the oil had a high wax content resulting in a “waxy” surface
accumulation of oil. This spill exhibited the typical challenges of platform blowouts—a very remote location, undetermined spill rate and volume, and the logistical
challenges needed to stop the flow of oil, which required subsea drilling. Chemical
dispersants also played an important role in reducing the amount of surface oiling
and contributed to the lack of any observed impacts on Ashmore and Cartier Reefs
(Storrie 2011). In the Montara spill, as with the Ixtoc blowout, only small amounts
of oil were measured to have been transported to the deep sea sediment (Burns and
Jones 2016).
The 1977 blowout of the Bravo well in the Ekofisk field of the North Sea also
released oil about 20 m above the sea surface (NOAA 2018a). This release was of
approximately 24,000 tonnes of oil (API gravity 35.7) (Audunson 1980). The
release occurred from the platform about 20 m above the sea surface, and despite
mild temperatures, extensive evaporation occurred as the oil was exposed to the
atmosphere before entering the water, resulting in an estimated 30–40% loss and a
measurable increase in density.
In contrast to the shallower spills, the high rate of release of oil and gas in deep
waters in the DWH oil spill and its extended release period drove a large investigative focus on the fate, transport, partitioning, and degradation of oil in the water
column and transport to the sea bottom (e.g., Boehm et al. 2016; Camilli et al. 2010;
Hazen et al. 2010; Stout et al. 2016; Valentine et al. 2010; Wade et al. 2016; Reddy
et al. 2012).
6.3 Properties of Oil Related to Fate and Transport
Oil and gasses released during a well blowout are a complex mixture of thousands
of hydrocarbon and non-hydrocarbon compounds with distinct properties. Though
oils released during blowouts have many chemical components and characteristics
in common, the specific chemical mixture that makes up the oil and gas and the
physical properties of the mixture of these components released during a subsurface
spill differ based on the oil reservoir from which the release occurs, the specific
6 The Importance of Understanding Transport and Degradation of Oil and Gasses…
dissolved lighter alkanes from the water column, as opposed to the heavier fraction
found in the surfaced oil, emphasizing the importance of examining the specific
composition of petroleum components to understand oil transport (Boehm and
Fiest 1979).
However, not all spills from offshore platforms involve subsea releases. The
Montara H1 well in the Timor Sea off the northwest coast of Australia blew out in
2009, releasing approximately 4,000 tonnes of oil over 74 days (Spies et al. 2017)
and producing a surface slick that was reported to travel approximately 35 km from
the location of the release (Burns and Jones 2016). However, unlike the previously
discussed deepwater releases, the release of this oil was from the platform above the
surface of the water, and hot oil and associated gas were exposed to the air before
reaching the water surface. Despite the released oil being classified as a light crude
(API gravity 34.6), the oil had a high wax content resulting in a “waxy” surface
accumulation of oil. This spill exhibited the typical challenges of platform blowouts—a very remote location, undetermined spill rate and volume, and the logistical
challenges needed to stop the flow of oil, which required subsea drilling. Chemical
dispersants also played an important role in reducing the amount of surface oiling
and contributed to the lack of any observed impacts on Ashmore and Cartier Reefs
(Storrie 2011). In the Montara spill, as with the Ixtoc blowout, only small amounts
of oil were measured to have been transported to the deep sea sediment (Burns and
Jones 2016).
The 1977 blowout of the Bravo well in the Ekofisk field of the North Sea also
released oil about 20 m above the sea surface (NOAA 2018a). This release was of
approximately 24,000 tonnes of oil (API gravity 35.7) (Audunson 1980). The
release occurred from the platform about 20 m above the sea surface, and despite
mild temperatures, extensive evaporation occurred as the oil was exposed to the
atmosphere before entering the water, resulting in an estimated 30–40% loss and a
measurable increase in density.
In contrast to the shallower spills, the high rate of release of oil and gas in deep
waters in the DWH oil spill and its extended release period drove a large investigative focus on the fate, transport, partitioning, and degradation of oil in the water
column and transport to the sea bottom (e.g., Boehm et al. 2016; Camilli et al. 2010;
Hazen et al. 2010; Stout et al. 2016; Valentine et al. 2010; Wade et al. 2016; Reddy
et al. 2012).
6.3 Properties of Oil Related to Fate and Transport
Oil and gasses released during a well blowout are a complex mixture of thousands
of hydrocarbon and non-hydrocarbon compounds with distinct properties. Though
oils released during blowouts have many chemical components and characteristics
in common, the specific chemical mixture that makes up the oil and gas and the
physical properties of the mixture of these components released during a subsurface
spill differ based on the oil reservoir from which the release occurs, the specific
6 The Importance of Understanding Transport and Degradation of Oil and Gasses…